Cigarette filter

ABSTRACT

A cigarette filter having a reagent which chemically reacts with and removes a gaseous component of a smoke stream. The reagent contains functional groups covalently bonded to a non-volatile inorganic substrate which is incorporated in the filter. The filter can remove gaseous components such as aldehydes from tobacco smoke. Preferred functional groups are 3-aminopropylsilyl groups covalently bonded to silica gel (APS silica gel). The reagent can be contained in a space in the filter or incorporated in one or more filter elements such as tipping paper, shaped paper insert, mouthpiece plug, solid filter element, or free-flow filter element. The reagent can be part of or coated on paper such as tipping or filter paper or incorporated in non-paper filter elements formed from fibrous materials such as cellulose acetate or polypropylene fibers. Other preferred reagents include aminoethylaminopropylsilyl (AEAPS) silica gel and aminoethylaminoethylaminopropylsilyl (AEAEAPS) silica gel.

This is a 371 of PCT/US99/25490, filed on Oct. 29^(th), 1999, which inturn is a Continuation in Part of application Ser. No. 09/181,859, filedon Oct. 29^(th), 1998, now U.S. Pat. No. 6,209,547.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a cigarette filter. Moreparticularly, the invention relates to a cigarette filter that canselectively remove a gaseous component such as aldehydes from tobaccosmoke.

2. Description of the Related Art

A wide variety of materials have been suggested in the art as filtersfor tobacco smoke. Such filter materials include cotton, paper,cellulose, and certain synthetic fibers. These filter materials,however, only remove particulates and condensable components fromtobacco smoke. They have little or no effect in removing certain gaseouscomponents, e.g., aldehydes, from tobacco smoke.

In light of this, a number of additives have been proposed in the art tosupplement the performance of the filter materials. Exemplary additivesare mentioned in, for example, U.S. Pat. Nos. 2,815,761; 2,881,772;2,968,306; 3,003,504; and 3,354,886. Some of the additives known in theart are effective in removing certain amounts of gaseous components fromtobacco smoke. However, those additives also suffer from variousdrawbacks.

For example, U.S. Pat. No. 2,968,306 discloses the use of certain aminoacids, such as glycine, for removing aldehydes in tobacco smoke. It hasbeen discovered that while glycine can reduce the level of formaldehydein tobacco smoke, it is not stable in the cigarette filter manufacturingprocess. Moreover, it releases ammonia odor during storage.

Thus, it is an object of the present invention to provide cigarettefilter arrangements and, more particularly, cigarette filters that canselectively remove a gaseous component such as aldehydes from tobaccosmoke without the drawbacks or disadvantages associated with previouslyknown additives.

SUMMARY OF THE INVENTION

It has been surprisingly discovered that a reagent comprising at leastone reactive functional group covalently bonded to a non-volatileinorganic substrate is selective in removing a gaseous component such asaldehydes from tobacco smoke. It has also been surprisingly found thatthis system does not exhibit the drawbacks associated with additivesknown in the art. The reagent is preferably incorporated in a cigarettefilter wherein the reactive functional group chemically reacts with agaseous component of the smokestream to remove it from the smokestream.

The preferred functional group is an aminopropylsilyl group such as a3-aminopropylsilyl group. The preferred substrate is in particle form,and more preferably is silica gel. The most preferred functionalgroup/substrate arrangement (reagent) contains 3-aminopropylsilyl groupsbonded to silica gel (hereinafter referred to as “APS silica gel”). Thisreagent can selectively remove gaseous components such as polarcompounds (e.g., aldehydes and hydrogen cyanide) from tobacco smoke.Other preferred reagents include aminoethylaminopropylsilyl (AEAPS)silica gel and aminoethylaminoethyl aminopropylsilyl (AEAEAPS) silicagel.

A cigarette typically contains two sections, a tobacco-containingportion sometimes referred to as the tobacco or cigarette rod, and afilter portion which may be referred to as the filter tipping. Thereagent can be advantageously employed along the filter portion of thecigarette. For example, the APS silica gel can be incorporated into thefilter paper, i.e., paper located in the filter portion of thecigarette. The APS silica gel can also be incorporated into the fibersof the filter portion or formed into a filter plug incorporated in thefilter portion and/or the tobacco rod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective partially exploded view of a cigaretteconstructed in accordance with one embodiment of the present inventionwherein folded paper containing a reagent which chemically reacts with acomponent of cigarette smoke is inserted into a hollow portion of atubular filter element of the cigarette;

FIG. 2 is a perspective partially exploded view of another embodiment ofthe present invention wherein the reagent is incorporated in foldedpaper inserted into a hollow portion of a tubular filter element;

FIG. 3 is a perspective partially exploded view of another embodiment ofthe present invention wherein the reagent is incorporated in aplug-space-plug filter element;

FIG. 4 is a perspective partially exploded view of another embodiment ofthe present invention wherein the reagent is incorporated in athree-piece filter element having three plugs;

FIG. 5 is a perspective partially exploded view of another embodiment ofthe present invention wherein the reagent is incorporated in afour-piece filter element having a plug-space-plug arrangement and ahollow sleeve;

FIG. 6 is a perspective partially exploded view of another embodiment ofthe present invention wherein the reagent is incorporated in athree-part filter element having two plugs and a hollow sleeve;

FIG. 7 is a perspective partially exploded view of another embodiment ofthe present invention wherein the reagent is incorporated in a two-partfilter element having two plugs;

FIG. 8 is a perspective partially exploded view of another embodiment ofthe present invention wherein the reagent is incorporated in a filterelement of a cigarette used with an electrical smoking device;

FIG. 9 depicts the chemical structures of the starting materials, theintermediate products, and the final APS silica gel reagent of arepresentative process for preparing the reagent used in the invention;

FIG. 10 shows a graphic representation of silica gel wherein the typicalSi—O—Si bond angle is 145°, the Si—O bond length is about 1.62 Å and thetypical Si—Si distance is about 3.06 Å;

FIG. 11 shows a graphic representation of APS silica gel wherein thetypical Si—O—Si bond angle is 145°, the Si—O bond length is about 1.62 Åand the typical Si—Si distance is about 3.06 Å;

FIG. 12 depicts the chemical structures of the starting materials, theintermediate products, and the final AEAPS silica gel;

FIG. 13 depicts the chemical structures of the starting materials, theintermediate products, and the final AEAEAPS silica gel; and

FIG. 14 shows a chemical formula representation of how the formaldehydecan be chemically bonded to the APS silica gel when cigarette smokecomes into contact with the APS silica gel.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a filter arrangement which is effective inremoving a component of cigarette smoke by chemically reacting a reagenttherewith. The reagent preferably comprises at least one reactivefunctional group. In order to prevent the reagent or its reactionproduct with the targeted cigarette smoke component from being carriedinto the cigarette smoke stream, the functional group is covalentlybonded to an inorganic non-volatile substrate. Such an arrangement isadvantageous over filter arrangements wherein gaseous components areabsorbed, adsorbed, or otherwise non-chemically removed from a smokestream. Such non-chemically removed components may be removed onlytemporarily and could reenter the smoke stream or if reacted with avolatile reagent, provide products that are themselves volatile andhence could reenter the smoke stream. According to the presentinvention, because the reactive functional group is covalently bonded tothe substrate, once the gaseous component chemically reacts with thereagent, the removed component (and its reaction products) can beprevented from reentering the smoke stream.

The following explanation is presented in the context of the mostpreferred embodiment in which the reagent is APS silica gel. Withoutwishing to be bound by theory, it is believed that the APS silica gelcontains primary amine groups. Under ordinary smoking conditions, theprimary amine groups chemically react with and covalently bond to thealdehydes in tobacco smoke. The aldehydes are thus selectively removedfrom the tobacco smoke. Further, since the reactive functional groupsand their resulting products from reaction with aldehydes are covalentlybonded to the silica gel which is non-volatile, the mainstream tobaccosmoke is essentially free of APS silica gel as well as the aldehydeswhich are bonded thereto.

Aldehydes in tobacco smoke that can be selectively removed by thereagent of the invention include, but are not limited to formaldehyde,acetaldehyde, acrolein, malonaldehyde, crotonaldehyde, etc.

In a first preferred embodiment, the reagent such as APS silica gel isincorporated into or onto a support such as paper (e.g., tipping paper)that is located along a filter portion of a cigarette. As will berecognized by persons skilled in the art, such paper can be used, forexample, as a wrapper or a liner in the filter portion of the cigarette.The reagent such as APS silica gel can also be loaded onto a supportsuch as lightly or tightly folded paper inserted into a hollow portionof the cigarette filter. The support is preferably in the form of asheet material such as crepe paper, filter paper, or tipping paper.However, other suitable support materials such as organic or inorganiccigarette compatible materials can also be used.

FIG. 1 illustrates a cigarette 2 having a tobacco rod 4, a filterportion 6, and a mouthpiece filter plug 8. As shown, the APS silica gelreagent can be loaded onto folded paper 10 inserted into a hollow cavitysuch as the interior of a free-flow sleeve 12 forming part of the filterportion 6.

FIG. 2 shows a cigarette 2 having a tobacco rod 4 and a filter portion6, wherein the folded paper 10 is located in the hollow cavity of afirst free-flow sleeve 13 located between the mouthpiece filter 8 and asecond free-flow sleeve 15. The paper 10 can be used in forms other thanas a folded sheet. For instance, the paper 10 can be deployed as one ormore individual strips, a wound roll, etc. In whichever form, a desiredamount of reagent such as APS silica gel can be provided in thecigarette filter portion by a combination of the coated amount ofreagent/area of the paper and/or the total area of coated paper employedin the filter (e.g., higher amounts of APS silica gel can be providedsimply by using larger pieces of coated paper). In the cigarettes shownin FIGS. 1 and 2, the tobacco rod 4 and the filter portion 6 are joinedtogether with tipping paper 14. In both cigarettes, the filter portion 6may be held together by filter overwrap 11.

The reagent such as APS silica gel can be incorporated into the filterpaper in a number of ways. For example, the APS silica gel can be mixedwith water to form a slurry. The slurry can then be coated ontopre-formed filter paper and allowed to dry. The filter paper can then beincorporated into the filter portion of a cigarette in the manner shownin FIGS. 1 and 2. Alternatively, the dried paper can be wrapped into aplug shape and inserted into a filter portion of the cigarette. Forexample, the paper can be wrapped into a plug shape and inserted as aplug into the interior of a free-flow filter element such as apolypropylene or cellulose acetate sleeve. In another arrangement, thepaper can comprise an inner liner of such a free-flow filter element.

Alternatively and more preferably, the reagent such as APS silica gel isadded to the filter paper during the paper-making process. For example,the APS silica gel can be mixed with bulk cellulose to form a cellulosepulp mixture. The mixture can be then formed into filter paper accordingto methods known in the art.

In another preferred embodiment of the present invention, the reagentsuch as APS silica gel is incorporated into the fibrous material of thecigarette filter portion itself. Such filter materials include, but arenot limited to, fibrous filter materials including paper, celluloseacetate fibers, and polypropylene fibers. This embodiment is illustratedin FIG. 3, which shows a cigarette 2 comprised of a tobacco rod 4 and afilter portion 6 in the form of a plug-space-plug filter having amouthpiece filter 8, a plug 16, and a space 18. The plug 16 can comprisea tube or solid piece of material such as polypropylene or celluloseacetate fibers. The tobacco rod 4 and the filter portion 6 are joinedtogether with tipping paper 14. The filter portion 6 may include afilter overwrap 11. The filter overwrap 11 contains traditional fibrousfilter material and reagent such as APS silica gel can be incorporatedin or on the filter overwrap 11 such as by being coated thereon.Alternatively, the APS silica gel can be incorporated in the mouthpiecefilter 8, in the plug 16, and/or in the space 18. Moreover, the APSsilica gel can be incorporated in any element of the filter portion of acigarette. For example, the filter portion may consist only of themouthpiece filter 8 and the APS silica gel can be incorporated in themouthpiece filter 8 and/or in the tipping paper 14.

FIG. 4 shows a cigarette 2 comprised of a tobacco rod 4 and filterportion 6. This arrangement is similar to that of FIG. 3 except thespace 18 is filled with granules of APS silica gel or a plug 15 made ofmaterial such as fibrous polypropylene or cellulose acetate containingAPS silica gel. As in the previous embodiment, the plug 16 can be hollowor solid and the tobacco rod 4 and filter portion 6 are joined togetherwith tipping paper 14. There is also a filter overwrap 11.

FIG. 5 shows a cigarette 2 comprised of a tobacco rod 4 and a filterportion 6 wherein the filter portion 6 includes a mouthpiece filter 8, afilter overwrap 11, tipping paper 14 to join the tobacco rod 4 andfilter portion 6, a space 18, a plug 16, and a hollow sleeve 20. The APSsilica gel can be incorporated into one or more elements of the filterportion 6. For instance, the APS silica gel can be incorporated into thesleeve 20 or granules of the APS silica gel can be filled into the spacewithin the sleeve 20. If desired, the plug 16 and sleeve 20 can be madeof material such as fibrous polypropylene or cellulose acetatecontaining APS silica gel. As in the previous embodiment, the plug 16can be hollow or solid.

FIGS. 6 and 7 show further modifications of the filter portion 6. InFIG. 6, cigarette 2 is comprised of a tobacco rod 4 and filter portion6. The filter portion 6 includes a mouthpiece filter 8, a filteroverwrap 11, a plug 22, and a sleeve 20, and the APS silica gel can beincorporated in one or more of these filter elements. In FIG. 7, thefilter portion 6 includes a mouthpiece filter 8 and a plug 24, and theAPS silica gel can be incorporated in one or more of these filterelements. Like the plug 16, the plugs 22 and 24 can be solid or hollow.In the cigarettes shown in FIGS. 6 and 7, the tobacco rod 4 and filterportion 6 are joined together by tipping paper 14.

Various techniques can be used to apply the reagent such as APS silicagel to filter fibers or other substrate supports. For example, the APSsilica gel can be added to the filter fibers before they are formed intoa filter cartridge, e.g., a tip for a cigarette. The APS silica gel canbe added to the filter fibers, for example, in the form of a dry powderor a slurry by methods known in the art. If the APS silica gel isapplied in the form of a slurry, the fibers are allowed to dry beforethey are formed into a filter cartridge.

In another preferred embodiment, the reagent such as APS silica gel isemployed in a hollow portion of a cigarette filter. For example, somecigarette filters have a plug/space/plug configuration in which theplugs comprise a fibrous filter material and the space is simply a voidbetween the two filter plugs. That void can be filled with the APSsilica gel of the present invention. An example of this embodiment isshown in FIG. 3. The APS silica gel can be in granular form or can beloaded onto a suitable support such as a fiber or thread.

In another embodiment of the present invention, the reagent such as APSsilica gel is employed in a filter portion of a cigarette for use with asmoking device as described in U.S. Pat. No. 5,692,525, the entirecontent of which is hereby incorporated by reference. FIG. 8 illustratesone type of construction of a cigarette 100 which can be used with anelectrical smoking device. As shown, the cigarette 100 includes atobacco rod 60 and a filter portion 62 joined by tipping paper 64. Thefilter portion 62 preferably contains a tubular free-flow filter element102 and a mouthpiece filter plug 104. The free-flow filter element 102and mouthpiece filter plug 104 may be joined together as a combined plug110 with plug wrap 112. The tobacco rod 60 can have various formsincorporating one or more of the following items: an overwrap 71,another tubular free-flow filter element 74, a cylindrical tobacco plug80 preferably wrapped in a plug wrap 84, a tobacco web 66 comprising abase web 68 and tobacco flavor material 70, and a void space 91. Thefree-flow filter element 74 provides structural definition and supportat the tipped end 72 of the tobacco rod 60. At the free end 78 of thetobacco rod 60, the tobacco web 66 together with overwrap 71 are wrappedabout cylindrical tobacco plug 80. Various modifications can be made toa filter arrangement for such a cigarette incorporating the reagent ofthe invention.

In such a cigarette, the reagent such as APS silica gel can beincorporated in various ways such as by being loaded onto paper or othersubstrate material which is fitted into the passageway of the tubularfree-flow filter element 102 therein. It may also be deployed as a lineror a plug in the interior of the tubular free-flow filter element 102.Alternatively, the reagent such as APS silica gel can be incorporatedinto the fibrous wall portions of the tubular free-flow filter element102 itself. For instance, the tubular free-flow filter element or sleeve102 can be made of suitable materials such as polypropylene or celluloseacetate fibers and the reagent such as APS silica gel can be mixed withsuch fibers prior to or as part of the sleeve forming process.

In another embodiment, the reagent such as APS silica gel can beincorporated into the mouthpiece filter plug 104 instead of in theelement 102. However, as in the previously described embodiments,according to the invention, the reagent such as APS silica gel may beincorporated into more than one component of a filter portion such as bybeing incorporated into the mouthpiece filter plug 104 and into thetubular free-flow filter element 102.

The filter portion 62 of FIG. 8 can also be modified to create a voidspace into which the reagent such as granular APS silica gel can beinserted.

As explained above, the APS silica gel can be incorporated in varioussupport materials. When the APS silica gel is used in filter paper, thesilica gel beads or particles may have an average particle diameter of10 to 100 μm, preferably 40 to 50 μm. When the APS silica gel is used infilter fibers or other mechanical supports, larger silica gel particlesmay be used. Such particles preferably have a mesh size from 25 to 60 ,and more preferably from 35 to 60 mesh. The silica gel particlespreferably have an average pore size of about 40 to about 250 Å, andmore preferably, about 150 Å.

The amount of APS silica gel employed in the cigarette filter by way ofincorporation on a suitable support such as filter paper and/or filterfibers depends on the amount of aldehydes in the tobacco smoke and theamount of aldehydes desired to be removed. As an example, the filterpaper and the filter fibers may contain from 10% to 50% by weight of theAPS silica gel.

Any commercially available APS silica gel such as that available fromJ.T. Baker Chemical Co., Philipsburg, N.J., can be used in the presentinvention. It should be noted that the J.T. Baker product is “capped.”This means that the free silica gel surface, i.e., the surface that hasnot been covalently bonded to the APS silica gel groups, is made to benon-polar by coverage with hydrophobic groups.

The APS silica gel can also be made, for example, by mixingaminopropyltriethoxysilane, more preferably3-aminopropyltriethoxysilane, with silica gel in a water and ethanolsolvent. Other solvents, such as toluene, can also be used. The mixtureis heated for several hours to allow the 3-aminopropyltriethoxysilane toreact with and chemically bond to the silica gel surface. The reactionmixture is then decanted to obtain a reaction product comprising the APSsilica gel. The reaction product is subsequently rinsed with a solvent,and dried in an oven at an elevated temperature such as around 100° C.or above. Although the rinsing and drying steps are optional, the dryingstep is preferred. Unlike the J.T. Baker product, the APS silica gelmade by this method is not “capped.”

The above paragraph describes a process routine which may be practicedwith other aminopropyltrialkoxysilanes, such as3-aminopropyltrimethoxysilane.

The APS silica gel can also be prepared by the following more specificprocedure. A suspension of the chosen silica gel is rapidly stirred in asolution of water and ethanol. To that mixture is added a3-aminopropyltrialkoxysilane compound, preferably3-aminopropyltriethoxysilane. The 3-aminopropyltrialkoxysilane can beadded before, during, or after heating. The 3-aminopropyltrialkoxysilaneis preferably pre-diluted with anhydrous ethanol. The resulting mixtureis then heated, preferably to the boiling point. In the most preferredembodiments, the ethanol is distilled off and replaced with water. Thesolids are isolated by a procedure such as filtration and with anoptional solvent rinse, preferably water. The solids are then heated inan oven until water loss has proceeded to equilibrium with thesurroundings. Typical embodiments entail heating overnight at about 105°C.

FIG. 9 depicts the most likely mechanism of the reaction that occurs inthe making of APS silica gel when 3-aminopropyltriethoxysilane andsilica gel are used as the starting materials. This mechanism is alsoapplicable to other 3-aminopropyltrialkoxysilanes. As shown, when3-aminopropyltriethoxysilane is contacted with water under appropriateconditions, the ethoxy groups are replaced with hydroxyl so that a3-aminopropyltrihydroxysilane intermediate is obtained. Thatintermediate is also believed to undergo a conformational change (whichstabilizes the monomeric form sufficiently to allow it to be used inaqueous medium) before reacting with the silica gel, as shown in FIG. 9.FIG. 9 further shows the structure of the intermediate reaction productof 3-aminopropyltrihydroxysilane and silica gel. FIG. 9 finally showsthe cross-linked APS silica gel product after curing. The curing causesthe loss of hydroxyl groups to result in at least a doubly linkedsilicon anchor for the reactive group.

As shown in FIG. 9, each silicon atom of silica gel is tetrahedrallycoordinated by four oxygen atoms, which are either singly bonded to twosilicon atoms or to a silicon and a proton (OH). The size of the ringcan vary, but is typically about 150 Å.

The 3-aminopropyltriethoxysilane can be obtained commercially from DowCorning Corp. The silica gel can be obtained commercially from the GraceDavison Division of W.R. Grace & Co.

EXPERIMENTAL EXAMPLES Preparation of APS Silica Gel Material

Grace Davison 646 (35×60 Mesh, 150-angstrom pore size) Silica Gel (circa1700 to 2000 grams) was placed into a 12-liter Pyrex glass kettle.Distilled water (4 liters) and 95% ethanol (2 liters; 100% ethanol isalso acceptable) was added. A clamp-on head had a central neck for thestirring-rod, and three peripheral necks for reagent addition and vaporexit. A stainless steel paddle stirrer was attached to a high-torque (50inch-pound) digitally controlled stirrer. The high torque stirrer neededto be double-clamped to a sturdy rack system, and served as the point ofreference with respect to the kettle. The latter was raised and loweredby a system of “Lab-Jacks,” and positioned precisely with respect to thefixed stirrer-rod. The stirrer blade needs to be fairly close to thekettle bottom, but not touching. The blade must never touch the bottomeven during “bumping” induced rebound of the flask/kettle. The flaskneeds to be restrained to prevent motion during “bumping,” which isunavoidable, but which the stirring minimizes. A plastic bearing wasfound to be advantageous since stainless steel bearings were found to beprone to seizing up, and glass bearings were prone to breakage. Themixture was stirred at 200 to 300 RPM, and heated (12 liter mantle, dualheating zone, 100 volts each zone). 3-aminopropyltriethoxysilane (1×500gram bottle), diluted with 100% ethanol (1 liter, including therinsings) was added as quickly as possible to the stirred heatedmixture. (Higher levels of APS functional group incorporation could beachieved by increasing the amount of reagent used).

The ethanol was distilled off. When about 2 liters of aqueous ethanoldistillate had collected, water (2 liters) was added to the reaction torestore the original volume. Two more liters of distillate werecollected, and two more liters of replacement water were added. Theheating was shut off, and stirring was continued until bumping ceased.The mixture was left to cool overnight. The apparatus was dismantled,and the silica was swirled manually and dumped into 4 liter plasticbeakers, using recycled supernatant liquid to complete the removal ofsolids. The solids were filtered off onto large (18 to 24 cm diameter)Buchner funnels, with minimal water rinsing (a few hundred millilitersat most). After suction had removed most of the liquid, the moist solidswere transferred to stainless steel trays, to dry overnight at 105° C.in an oven.

Depending on the amount of 3-aminopropyltriethoxysilane employed,relative to the starting silica gel, the dried products showed nominalweight gains ranging from about 8% to about 24%. One of the batches usedin the examples below was prepared from 1692.4 grams of Grace DivisionSilica Gel 646 and 500.1 grams of 3-aminopropytrietoxysilane under thegeneral conditions described above. After drying, 1891 grams of APSsilica was obtained. A sample was analyzed for C, H, and N. Found: C,4.21%; H, 1.37%; N, 1.58%. Based on the nitrogen analysis, the3-aminopropyl content of the silica was 6.55% by weight of producttotal.

Cigarette Testing

Several tests were conducted to determine the ability of the cigarettefilter of the present invention to remove aldehydes from tobacco smokeas compared to conventional devices. The tests measured the amount ofaldehydes removed from the wholestream smoke after the cigarette wasfully smoked. WS represents the amount, in %, of aldehydes removed fromthe wholestream smoke after all the smoke has been collected andanalyzed. TPM represents the amount, in mg/cigarette, of particulatematerial collected in the filter portion of the cigarette.

In the following tests, the silica gels used showed a nominal weightgain of about 8 to 25% from the original silica gel during themanufacturing process outlined above. Based on the tests below, apreferred weight gain is around 8 to 16, preferably 10 to 15 wt. %. Itis important to note that this weight gain does not refer to weight gainas a result of removing aldehydes. It refers to weight gain from thereaction that adds functional groups such as APS functional groups tothe silica gel. APS silica gels that are especially effective whenemployed in accordance with this invention exhibit a nitrogen contentpreferably in the range of about 1 to 3 percent by weight, and morepreferably in the range of about 1.5 to about 2.1 percent.

Example 1

Filter sections of cigarettes were constructed in accordance with FIG. 1and with the tobacco rod section of FIG. 8. A filter section constructedin accordance with the invention identified as Sample 2 contained 16.5mg of APS silica gel on a folded piece of filter paper 10 (17 mm×23 mm)inserted in the hollow portion of the tubular filter 12. Another filtersection constructed in accordance with the invention identified asSample 3 contained 21 mg of APS silica gel on a folded piece of filterpaper 10 (22 mm×23 mm) inserted into the hollow portion of the tubularfilter 12. A comparative filter section using a folded piece of thefilter paper (17 mm×23 mm) paper (without any APS silica gel) fittedinto the hollow portion of the tubular filter was constructed as acontrol and identified as Sample 1. For Samples 2 and 3, 15 cigaretteswere made for TPM measurements and 9 were made for WS measurements. Forcontrol Sample 1, 15 cigarettes were made for TPM measurements and 15for WS measurements. The results are shown in Table 1 below.

TABLE 1 SAMPLE TPM WS 1 2.85 Control 2 2.83 ˜61% 16.5 mg reagent 3 3.11˜78% 21.0 mg reagent

Example 2

Cigarettes similar to those tested in Example 1 included a shortersection containing the APS silica gel. In Samples 1-3, the filtersection was constructed in accordance with FIG. 2 and included a 16 mmsleeve 13, a 7 mm sleeve 12, and a 7 mm filter plug 8. The sleeve 12contained a folded sheet (7 mm×75 mm) of APS silica gel coated oruncoated paper. Three samples identified as control Sample 1 (uncoatedpaper), Sample 2 (paper coated with 11 mg APS silica gel), and Sample 3(paper coated with 22 mg APS silica gel) were tested. 15 cigarettes ofeach sample were made for TPM measurement and 9 for WS measurement. Theresults are shown in Table 2 below.

TABLE 2 SAMPLE TPM WS 1 3.37 (Control) 2 3.14 ˜69% 11 mg reagent 3 2.35˜78% 22 mg reagent

Example 3

Cigarettes were constructed in accordance with a more conventionalcigarette having a tobacco rod like that shown in FIG. 2 and aconventional filter element. Sample 1 is a control sample without APSsilica gel and Sample 2 contained 50 mg APS silica gel in the filterelement. The WS was measured for each and the results are shown in Table3.

TABLE 3 SAMPLE WS 1 Control 2 ˜71% 50 mg reagent

Example 4

Cigarettes were constructed in accordance with FIG. 8 having APS silicagel contained in the mouthpiece filter. Sample 1 is a control samplewhich did not include APS silica gel and Samples 2 and 3 contained APSsilica gel in the mouthpiece filter 104 which was 7 mm long. The samplesalso included a sleeve 102 adjacent the mouthpiece filter which was 23mm long and constructed of polypropylene. In Sample 3, 11 mg APS silicagel was included in an additional polypropylene sleeve 74 having alength of 7 mm and located in the tobacco rod at an end thereof adjacentthe filter element. The WS was measured for each and the results areshown in Table 4.

TABLE 4 SAMPLE WS 1 Control 2 Polypropylene mouthpiece filter with 12 mgreagent ˜46% 3 Polypropylene mouthpiece filter with 11 mg reagent ˜41%

Example 5

Cigarettes were constructed in accordance with FIG. 8 having APS silicagel contained in various filter elements. The cigarettes were tested forWS and TPM levels and the results are shown in Table 5 below.

TABLE 5 SAMPLE TPM WS 1 Control 2 Polypropylene sleeve 102 with 40 mg5.88 ˜38% reagent and second polypropylene sleeve 74 with 11 mg reagent3 Polypropylene sleeve 102 with 40 mg 5.11 ˜35% reagent 4 Celluloseacetate sleeve 102 with 50 mg 4.71 ˜35% reagent 5 Polypropylene sleeve102 with 25 mg 5.73 ˜33% reagent and 25 mg carbon

All samples had a 23 mm long sleeve 102 in the filter portion and a 7 mmlong mouthpiece filter 104. In Sample 2, the second sleeve 74 containingthe APS silica gel was located in the tobacco rod adjacent the filterportion and had an inner diameter of 4.0 mm. In Samples 3-5, a secondsleeve 74 similar to that of Sample 2 but without the APS silica gel hadan inner diameter of 3.5 mm.

Example 6

Cigarettes were constructed in accordance with the plug-space-plugembodiment shown in FIG. 5. In each cigarette, the tubular free-flowfilter element 20 was 13 mm long, the filter plug 8 was 5 mm long, thefilter plug 16 was 7 mm long, and the void space 18 was 5 mm long.Control Samples 1 and 3 contained 50 mg of silica gel without any APSsilica gel in the void space 18 and Samples 2 and 4 included APS silicagel particles weighing 50 mg in the void space 18. WS was measured andthe results are shown in Table 6 below.

TABLE 6 SAMPLE WS 1 (Control) ˜50% 2 ˜87% 3 (Control) ˜78% 4 over 93%  

Example 7

The cigarettes used for Samples 2 and 3 in Table 7 below wereconstructed in accordance with the embodiments shown in FIGS. 6 and 7,respectively. In Sample 2, the tubular filter element 20 was 16 mm long,the filter plug 8 was 7 mm long, and the solid plug 22 was 7 mm long andcomprised of a hand rolled mixture of APS silica gel and polypropylenefibers. In Sample 3, the plug 24 was 23 mm long and comprised of a handrolled mixture of APS silica gel and polypropylene fibers and the filterplug 8 was 7 mm long. Sample 1 was a control cigarette. Measurementswere made of TPM and WS. The results are shown in Table 7 below.

TABLE 7 SAMPLE TPM WS 1 2 3.92 ˜66% 3 Not tested ˜81%

According to the invention, the surface of silica gel can be chemicallymodified to achieve desired selective filtration properties. In the caseof APS silica gel, the aminopropylsilyl group is attached to the silicagel skeleton by one or more covalent silicon-oxygen-silicon bonds. Theprimary amine group at the terminal (exposed or free) end of theaminopropylsilyl group readily reacts with aldehydes and ketones. Theprimary amine reacts with the aldehyde to form an imine and/or othercovalently bonded derivatives of the aldehyde. The imine group or othercovalently bonded derivative of the aldehyde remains anchored to thesilica gel and thus the formation of such derivatives serves toeffectively remove the aldehydes and ketones and their reaction productsfrom cigarette smoke. The primary amine group also reacts with hydrogencyanide through an acid-base reaction thus reducing the levels of thiscompound in the cigarette smoke.

Silica gel is a variably hydrous form of silicon dioxide sometimescalled “silicic acid’ which can be prepared by precipitation from anacid solution of sodium silicate. The silica gel can be characterized asa porous disordered three-dimensional polymer of siloxane tetrahedra,forming sheets, ribbons, chains and frameworks with various pore-sizespermeating the whole, formed by the variable nature of the cross-linkingof the overall three-dimensional structure. Each silicon atom is bondedto four oxygen atoms, at the corners of a tetrahedron. The oxygen atomsare mostly bonded to two silicon atoms but some can be bonded to asingle silicon atom and one hydrogen atom to generate a “silanol”functionality. The majority of oxygen atoms are “siloxane” oxygen atomswhich are bonded to two silicon atoms. Some silicon atoms called“germinal” silanediols are bonded to two silanol oxygens. The vastmajority of silanol groups consist of a silicon atom with one hydroxylgroup and three siloxane oxygens. Such silanols may be isolated from oneanother but when adjacent each other are referred to as “vicinal”silanols (oxo-bis-silanols). Such silanol functionality provides a pointof attachment for derivatizing groups such as 3-aminopropylsilyl. FIG.10 shows a graphic representation of silica gel wherein the typicalSi—O—Si bond angle is 145°, the Si—O bond length is about 1.62 Å and thetypical Si—Si distance is about 3.06 Å.

APS silica gel can be characterized as silica gel which has beenmodified at some of the hydroxyl groups by the derivatizing reagent3-aminopropyltriethoxysilane which permanently attaches3-aminopropylsilyl (APS) groups to the porous silica gel framework. Theattached 3-aminopropylsilyl groups can react with targeted carbonylgroup containing substrates. FIG. 11 shows a graphic representation ofAPS silica gel wherein the typical Si—O—Si bond angle is 145°, the Si—Obond length is about 1.62 Å and the typical Si—Si distance is about 3.06Å. The 3-aminopropylsilyl groups can be considered basic in that theycan remove acids such as hydrogen cyanide from mainstream cigarettesmoke. In preparing such APS silica gel it is preferred that the silicagel have a large average pore diameter. For instance, whereas“desiccant” silica gel has a pore size on the order of 20 Å, a preferredpore size for the APS silica gel is on the order of 60 to 150 Å. Largepore-sized silica gel can be obtained from the Davison Chemical Divisionof the W.R. Grace & Company, Baltimore, Md.

One technique for making such large pore-sized silica gel is bypreparing a sodium silicate solution containing dilute sulfuric acid,allowing the solution to gel over time, washing with water (for severaldays), drying and grinding the silica gel. In converting the silica gelinto APS silica gel, the silica gel of the desired particle size can beheated with the derivatizing reagent 3-aminopropyltriethoxysilane in asolvent such as water, ethanol, toluene or the like, and heat-drying thereaction product to “cure” the product. Any unused reagent can berecycled during production of other batches of APS silica gel.

The APS silica gel can be prepared using other derivatizing reagents.For instance, another derivatizing reagent which can be used is3-aminopropyltrimethoxysilane which generates methanol during themanufacturing process. In contrast, 3-aminopropyltriethoxysilanegenerates ethanol. In addition, the silica gel can be modified toincorporate groups in addition to or instead of the APS. For example,the silica gel can be modified to form aminoethylaminopropylsilyl(AEAPS) silica gel which can be made usingN-[3-(trimethoxysilyl)propyl]-ethylenediamine (Chemical AbstractsService Registry No. 1760-24-3) as the derivatizing reagent. FIG. 12depicts the chemical structures of the starting materials, theintermediate products, and the final AEAPS silica gel. Alternatively,the silica gel can be modified to formaminoethylaminoethylaminopropylsilyl (AEAEAPS) silica gel which can bemade using N¹-[3-(trimethoxysilyl)propyl]-diethylenetriamine (ChemicalAbstracts Service Registry No. 35141-30-1) as the derivatizing reagent.FIG. 13 depicts the chemical structures of the starting materials, theintermediate products, and the final AEAEAPS silica gel. The abovedescribed APS, AEAPS and AEAEAPS surface modified silica gels can bemade in commercial quantities by economic manufacturing conditions. Itis contemplated that any covalently bonded amine group attached tosilica such as homologues or analogues with additional aminefunctionality can also be used as a component of an air filter such as acigarette filter in accordance with the invention.

During filtration, the APS silica gel can permanently remove selectgaseous components from an airstream such as mainstream tobacco smoke.For instance, by incorporating the APS silica gel in a cigarette filter,cigarette paper, tobacco filler and/or tobacco containing sheet materialof a cigarette, the APS silica gel can be used to selectively removeformaldehyde from tobacco smoke. FIG. 14 shows a chemical formularepresentation of how the formaldehyde can be chemically bonded to theAPS silica gel when cigarette smoke comes into contact with the APSsilica gel.

While the invention has been described with reference to preferredembodiments, it is to be understood that variations and modificationsmay be resorted to as will be apparent to those skilled in the art. Suchvariations and modifications are to be considered within the purview andscope of the invention as defined by the claims appended hereto. Forexample, the ring structure depicted in FIG. 9 is representative of awide range of ring sizes present within the highly disordered silica gelstructure, and is not intended to exclude other sizes of ring fromconsideration as components of the matter covered by this patentapplication.

What is claimed is:
 1. A cigarette filter comprising a reagentconsisting essentially aminoethylaminopropylsilyl silica gel oraminoethylaminoethylaminopropylsilyl silica gel wherein the reagentchemically reacts with a gaseous component of a smoke stream to removesaid gaseous component from said smoke stream.
 2. The cigarette filteraccording to claim 1, wherein the filter is attached to a tobacco rod bytipping paper or the reagent is incorporated in one or more cigarettefilter parts selected from the group consisting of tipping paper, shapedpaper insert, a plug, a space, or a free-flow sleeve.
 3. The cigarettefilter according to claim 1, wherein the reagent comprises particles ora shaped article of silica gel.
 4. The cigarette filter according toclaim 1, wherein the gaseous component to be removed from saidsmokestream is polar such as an aldehyde.
 5. The cigarette filteraccording to claim 1, wherein said reagent is incorporated in cigarettefilter paper located within a free-flow filter, the filter paperoptionally having a three-dimensional shape and/or the filter paperbeing a liner on the interior of a hollow tubular element.
 6. Thecigarette filter according to claim 1, wherein said reagent isincorporated with cellulose acetate fibers and/or polypropylene fibersforming a plug or a free-flow filter element.
 7. The cigarette filteraccording to claim 1, wherein said reagent is incorporated in a cavityor said reagent is incorporated in at least one of a mouthpiece filterplug and a tubular filter element adjacent to said mouthpiece filterplug or said reagent is incorporated in at least one of a mouthpiecefilter plug, a first tubular filter element adjacent to said mouthpiecefilter plug, and a second tubular filter element adjacent to the firsttubular element or said reagent is incorporated in at least one part ofa three-piece filter including a mouthpiece filter plug, a first filterplug adjacent to said mouthpiece filter plug, and a second filter plugadjacent to the first filter plug.
 8. The cigarette filter according toclaim 1, wherein said silica gel has an average particle diameter of 10to 50 μm or said silica gel is in the form of 25 to 60 mesh particles.9. The cigarette filter according to claim 1, wherein said reagent isincorporated in a cavity or said reagent is incorporated in at least oneof a mouthpiece filter plug and a tubular filter element adjacent tosaid mouthpiece filter plug or said reagent is incorporated in at leastone of a mouthpiece filter plug, a first tubular filter element adjacentto said mouthpiece filter plug, and a second tubular filter elementadjacent to the first tubular element or said reagent is incorporated inat least one part of a three-piece filter including a mouthpiece filterplug, a first filter plug adjacent to said mouthpiece filter plug, and asecond filter plug adjacent to the first filter plug.
 10. The cigarettefilter according to claim 1, wherein the total nitrogen content of saidsilica gel is in the range of approximately 1 to 3 percent by weight,preferably 1.5 to 2.1 percent by weight.
 11. The cigarette filteraccording to claim 1, wherein the reagent is prepared by reacting silicagel with an aqueous or non-aqueous solution containingN-[3-(trimethoxysilyl)propyl]-ethylenediamine orN¹-[3-(trimethoxysilyl)propyl]-diethylenetriamine.
 12. A method ofmanufacturing a cigarette filter which is useful for removing a gaseouscomponent of tobacco smoke, comprising steps of: preparing a reagentconsisting essentially of aminoethylaminopropylsilyl silica gel oraminoethylaminoethylaminopropylsilyl silica gel; and incorporating thereagent in a cigarette filter wherein the reagent chemically reacts witha gaseous component of tobacco smoke to remove said gaseous componentfrom said gas mixture.
 13. The method according to claim 12, furthercomprising attaching the cigarette filter to a tobacco rod with tippingpaper or the reagent is incorporated in one or more cigarette filterparts selected from the group consisting of tipping paper, shaped paperinsert, a plug, a space, or a free-flow sleeve.
 14. The method accordingto claim 13, further comprising a step of attaching the filter paperwithin a free-flow filter of a cigarette such as by forming said filterpaper into a three-dimensional shape or attaching said filter paper as aliner on the interior of a hollow tubular element or combining saidreagent with fibers and forming a filter element from said reagent andfibers or combining said reagent with cellulose and/or polypropylenefibers and forming a plug or free-flow filter element or incorporatingsaid reagent in a cavity of said filter.
 15. The method according toclaim 12, further comprising a step of incorporating said reagent in atleast one of a mouthpiece filter plug and a tubular filter elementadjacent to said mouthpiece filter plug or incorporating said reagent inat least one of a mouthpiece filter plug, a first tubular filter elementadjacent to said mouthpiece filter plug, and a second tubular filterelement adjacent to the first tubular element or incorporating saidreagent in at least one part of a three-piece filter including amouthpiece filter plug, a first filter plug adjacent to said mouthpiecefilter plug, and a second filter plug adjacent to the first filter plug.16. The method according to claim 12, wherein said silica gel has anaverage particle diameter of at least 10 μm or said silica gel is in theform of particles having a mesh size of at least
 60. 17. The methodaccording to claim 12, wherein the silica gel is in the form ofparticles, the method further comprising a step of loading the silicagel particles on filter fibers or other mechanical supports, said silicagel particles having a mesh size of at least 60 and an average pore sizeof about 40 to about 250 Å or the silica gel comprises beads orparticles, the method further comprising a step of incorporating thesilica gel beads or particles in a support material, the silica gelbeads or particles having an average particle diameter of at least 10μm.
 18. The method according to claim 12, wherein the reagent isprepared by reacting silica gel with an aqueous or non-aqueous solutioncontaining N-[3-(trimethoxysilyl)propyl]-ethylenediamine orN¹-[3-trimethoxysilyl)propyl]-diethylenetriamine.
 19. A method ofremoving a gaseous component of tobacco smoke, comprising passing thetobacco smoke in contact with a cigarette filter comprising a reagentconsisting essentially of aminoethylaminopropylsilyl silica gel oraminoethylaminoethylaminopropylsilyl silica gel which chemically reactswith the gaseous component of the tobacco smoke and removes said gaseouscomponent from said tobacco smoke.
 20. The method according to claim 19,further comprising steps of burning tobacco and directing a gas streamcontaining the tobacco smoke through the cigarette filter such that thecomponent of the tobacco smoke to be removed is chemically reacted withthe reagent and prevented from reentering the gas stream.
 21. The methodaccording to claim 19, wherein the reagent is incorporated in one ormore cigarette filter parts selected from the group consisting of filterpaper, tipping paper, shaped paper insert, a plug, a space, or afree-flow sleeve, the tobacco smoke being passed through the one or morefilter parts.
 22. The method according to claim 19, wherein the reagentis effective to remove formaldehyde from the tobacco smoke.
 23. Themethod according to claim 19, wherein the reagent comprises particles ora shaped article, the tobacco smoke being passed through a mass of theparticles or through the shaped article.
 24. The method according toclaim 19, wherein the cigarette filter removes a polar gaseous componentsuch as a aldehyde.
 25. The method according to claim 19, wherein saidsilica gel has an average particle diameter of at least 10 μm or saidsilica gel is in the form of particles having a mesh size of at least 60and said tobacco smoke is passed through a mass of particles of saidsilica gel.
 26. The method according to claim 19, wherein said silicagel is incorporated with cellulose acetate fibers and/or polypropylenefibers and the tobacco smoke is a smoke stream from a burning cigarette.27. The method according to claim 19, wherein the cigarette filterincludes a space containing loose granules of said silica gel and thetobacco smoke passes through said loose granules or said silica gel isloaded on a support material and said tobacco smoke flows in contactwith said silica gel loaded on said support material.
 28. The methodaccording to claim 19, wherein the cigarette filter is part of amouthpiece filter plug, a tubular filter element, a solid plug, or anopen space, said tobacco smoke being passed through said filter.
 29. Themethod according to claim 19, wherein said tobacco smoke is passedthrough paper containing or coated with said silica gel or the tobaccosmoke is passed through a cigarette filter comprising fiber loaded withthe silica gel.
 30. The method according to claim 19, wherein the silicagel is in the form of particles on filter fibers or other mechanicalsupports, said particles having a mesh size of at least 60 and anaverage pore size of about 40 to about 250 Å, the tobacco smoke beingpassed through the cigarette filter containing the silica gel particlesand the fibers or other mechanical supports.
 31. The method according toclaim 19, wherein the silica gel comprises beads or particlesincorporated in a support material, the silica gel beads or particleshaving an average particle diameter of at least 10 μm, the tobacco smokebeing passed through the cigarette filter containing the silica gelbeads or particles.
 32. The method according to claim 19, furthercomprising steps of loading the silica gel onto fibrous material formingan air permeable cigarette filter body.
 33. The method according toclaim 19, wherein the reagent is covalently bonded to cigarette filterfibers in an amount of 10 to 50% by weight.
 34. The method according toclaim 19, wherein the reagent is prepared by reacting silica gel with anaqueous or non-aqueous solution containingN-[3-(trimethoxysilyl)propyl]-ethylenediamine orN¹-[3-(trimethoxysilyl)propyl]-diethylenetriamine.